Wavelength division multiplexed (WDM) optical communication systems (referred to as “WDM systems”) are systems in which multiple optical signals, each having a different wavelength, are combined onto a single optical fiber using an optical multiplexer circuit (referred to as a “multiplexer”). Such systems may include a transmitter circuit, such as a transmitter (Tx) photonic integrated circuit (PIC) having a transmitter component to provide a laser associated with each wavelength, a modulator configured to modulate the output of the laser, and a multiplexer to combine each of the modulated outputs (e.g., to form a combined output or WDM signal). The transmitter component may be configured to utilize a target wavelength for a particular transmission channel, but may actually transmit at a different wavelength. Dual-polarization (DP) (also known as polarization multiplex (PM)) is sometimes used in coherent optical modems. An optical transmitter may be associated with a polarization beam combiner (PBC) that combines two optical signals into a composite DP signal.
A WDM system may also include a receiver circuit having a receiver (Rx) PIC and an optical demultiplexer circuit (referred to as a “demultiplexer”) configured to receive the combined output and demultiplex the combined output into individual optical signals. Additionally, the receiver circuit may include receiver components to convert the optical signals into electrical signals, and output the data carried by those electrical signals.
The optical transmitter (Tx) and the optical receiver (Rx), in an optical communication system, may support communications over a number of wavelength channels. For example, a pair of optical transmitter/receiver may support ten channels, each spaced by, for example, 200 GHz. The set of channels supported by the optical transmitter and the optical receiver can be referred to as a channel grid. Channel grids for the optical transmitter and the optical receiver may be aligned to standardized frequencies, such as those published by the Telecommunication Standardization Sector (ITU-T). The set of channels supported by the optical transmitter and the optical receiver may be referred to as an ITU frequency grid. The set of channels may be aligned to non-standardized frequencies, such as an arbitrary grid that is determined based on network traffic that is to be transmitted and does not correspond to the ITU frequency grid, or the like.